1. Field of the Invention
The present invention relates to improvement of a ball bearing used in a small size fan utilized in various kinds of OA apparatus and so on.
2. Description of the Related Art
Where a large number of electronic circuits are contained in a casing such as in various kinds of OA apparatus, there is a fear that heat generated by electronic components therefrom leads to breakage of the electronic components. In order to avoid this, a vent hole is provided in a side wall of the casing for attaching a small size fan therein to radiate heat generated inside the casing to the outside.
An example of a conventional, commonly employed small size fan is described in the following by referring to FIG. 3. A reference numeral 1 denotes a casing. The casing 1 comprises a cylindrical venturi portion 2, the inside of which is slantingly formed and a bearing box 3 integral with the venturi portion 2. Two ball bearing 4 and 5 are provided inside a standing portion of the bearing box 3. The inner rings of the ball bearings 4 and 5 rotatably support an axis 6. A reference numeral 7 denotes a snap ring for preventing the axis 6 from coming off.
As shown in the figure, a knurl 8 is provided by being nicked on the upper portion of the axis 6. The portion where the knurl 8 is provided is inserted in molding manner at a boss 10 of an impeller 9. A plurality of fan blades 11 are radially attached on the periphery of the boss 10. A reference numeral 12 denotes a coil spring for applying suitable thrust pre-load to an inner ring of the ball bearing 5.
As shown in the figure, the boss 10 of the impeller 9 is substantially E-shaped in section, and the fan blades 11 are attached on the periphery of the boss 10. A yoke 13 is attached on the inside of the boss 10 for holding a magnet 14 which is cylindrical and circumferentially magnetized. A disc-like PC board 15 is provided on the periphery of the standing portion of the bearing box 3 for mounting electronic circuits and a set of components for a DC brushless motor (not shown) thereon. A reference numeral 16 denotes a lead wire for supplying electric power to the electronic circuits.
A stator 20 comprising a core 17, a coil 18 wound around the core 17, and an insulator 19 for holding the core 17 is supported at a portion above the PC board 15 and inside the magnet 14.
The axial flow motor of the above structure operates as follows. When power supply voltage is supplied to the electronic circuits via the lead wire 16, the core 17 of the stator 20 is magnetized in predetermined order, and, according to the relationship between a magnetic field generated by the magnetization and a magnetic field generated by the magnet 14, the impeller 9 rotates around the axis 6. Since the rotation allows the fan blades 11 to generate air flow in a predetermined direction inside the venturi portion 2 of the casing 1, heat generated inside a casing attaching the small size fan can be radiated to the outside.
With reference to the above-mentioned small size fan, when, for example, the length of the four sides of an enclosure is 80 mm, and the axial length is 25 mm, the dimensions of the bearings 4 and 5 used therein are generally in the order of 8 mm in outer diameter, 3 mm in inner diameter, and 4 mm in thickness. As shown in FIG. 4, each of the ball bearings comprises balls 21, an innner ring 22, an outer ring 23, and a cage 24. As the ball 21, six pieces are used. With regard to the cage 24, one called a corrugated type with a claw is used.
Here, with reference to the above-mentioned small size fan, an examination of the load borne by the ball bearing revealed that the radial load is 0.2 kg at the most. With regard to the thrust load, most of the thrust load is caused by the urging power by the coil spring 12, and the pressure of the coil spring 12 is set in the order of 0.4 kg. Therefore, the basic load rating of the conventionally used ball bearing far exceeds a required value, that is, the ball bearing has excessive durability. In addition, since the cage 24 is structured to sandwich the balls with two components 24a and 24b manufactured by press molding of a steel plate, the area of the components 24a and 24b contacting with the balls 21 is large, thereby increasing the friction torque during rotation. Further, there is a disadvantage that, since the claw 24c must be clamped in order to fix the two components 24a and 24b, the number of processes in assembling increases much more.
That is, the conventional ball bearing is not the most suitable for a small size fan, and there has been room for further improvement of the ball bearing for reducing the cost, and improving durability, weight, and so on, of a small size fan.